The present invention relates to a device making it possible to convey flat objects stacked in bundles, through a machine responsible for tying each of said bundles.
The invention finds a particularly advantageous application in the packaging field.
In the packaging industry, the manufacture of folding boxes is conventionally carried out on line, by folding and gluing blanks by means of machines commonly called folder-gluers. Usually, the folding boxes are delivered in the form of a continuous stream, so that it is appropriate to package them in bundles when said boxes are designed to be stored before their first use.
In this situation, it is known practice to package the folding boxes in the form of strapped bundles, that is to say stacks of boxes that are attached individually by means of one or more tying elements. Various types of strapping means can be used to accomplish this task, depending on whether it is desired, for example, to bind each bundle by means of at least one thin tying element such as a string, strap each bundle by means of at least one narrow tying element such as a strap, or wrap each bundle using at least one broad tying element such as a band.
In a standard strapping machine, two zones are of more particular importance. They are first of all the assembly zone which is situated at the entrance of the machine and which is designed for the formation of each bundle, and there is then the strapping zone which is positioned nearer to the heart of the machine, and which, for its part, is dedicated to the tying of each bundle. Naturally, a conveyance device is provided to ensure the individual movement of each bundle through the strapping machine, notably from the assembly zone to the strapping zone.
In practice, such a movement is conventionally carried out in two stages in order to be able to have reduced cycle times. This feature involves the existence of an intermediate zone, namely a transfer zone which is logically situated between the assembly zone and the strapping zone. However it may be, it is for this reason that this type of conveyance device usually uses two distinct conveying means.
In reality, first conveying means move each bundle from the assembly zone to the transfer zone, while second conveying means are responsible for moving said bundle from the transfer zone to the strapping zone. In this situation, the purpose of the first conveying means is primarily to rapidly clear the assembly zone in order to be able to begin forming another bundle as quickly as possible. The responsibility of the second conveying means is however to feed the strapping means with bundles with no idle time.
In view of this, a strapping machine is known notably from the prior art that is used to tie together folding boxes assembled in bundles, and which has such a device for conveying bundles. In this machine, the formation of each bundle is carried out by successive deposits of batches of boxes, in the middle of four bracket-shaped guides that are placed vertically at the four corners of the stack. The two downstream guides are provided with movable stops the retraction of which allows extraction to the front of the bundle. The first conveying means consist of a pneumatic pusher which is capable of pushing the bundle from behind when the latter is complete in order to extract it from the guides and bring it to the second conveying means. These second conveying means, for their part, take the form of an association of conveyor belts that consists of a horizontal belt, two vertical belts and one top conveyor belt which all turn in the same direction and at the same speed.
This type of conveyance device however has the drawback of being complicated to adjust, both in the position of the guides of the assembly zone, and in the synchronization of the conveyor belts of the second conveying means.
Another major drawback of such a conveyance device lies in the fact that it is insufficiently accurate in terms of guidance. Consideration here is given in particular to the poor effectiveness of the vertical guides of the assembly zone when the pneumatic pusher is set in motion, but also to that of the conveyor belts because of the friction that unavoidably occurs when the bundles pass.